Methods for powering portable devices through cables are known in the art. For instance, a battery-powered device may be charged by connecting it to a wall-plug adaptor including a power converter through a pluggable (removable) standardized cable, such as a Universal Serial Bus USB cable. A charger circuit in the battery-powered device is responsible for limiting the current delivered over the standardized cable in order to prevent over-heating of connectors and the cable itself. Being standardized, the cable connecting the wall-plug adaptor to the mobile device can be replaced with any other cable the connectors of which seem to conform to the same standard, but which is of lower quality (sub-standard cable). Therefore, the current limit has to be set low enough so that low-quality cables or an increased connector impedance, caused by connector wear over time or dirt caught between the plug and the receptacle, will not present a safety risk during charging. Other safety critical situations may arise if the power pins of two connectors are not properly connected to each other.
In existing solutions, the current limit is based on specifications of the relevant standard, e.g. specifications of the USB standard, and evaluations done by the device manufacturer.
However, such existing solutions do not account for removable cables of low quality, the connectors of which only seem to conform to the given standard (i.e. fit physically into respective receptacles of the mobile device and the wall-plug adaptor), but which themselves do not meet the specifications of the given standard (i.e. substandard cables). Using such removable cables may result in damage to the wall-plug adaptor or the battery-powered device. In the worst case, the wall-plug adapter, the cable, one of the connectors, or the charger circuit within the battery-powered device may be thermally destroyed. Moreover, such existing solutions do not account for an increase of the impedance of a cable caused by dust or by wear and tear. Also, fixedly setting the current limit on the basis of specifications of the relevant standard may not allow charging the battery-powered device with the highest possible current under all circumstances, in particular when taking into account safety margins. Thus, state of the art solutions may not be able to achieve the shortest possible charging time for the battery-powered device.